The present invention relates to a hub for a syringe that is co-molded with a cannula and a method for forming or co-molding the cannula to the syringe barrel. The cannula is preferably a fine gauge cannula, which is co-molded to the syringe barrel to form a staked needle device.
The process of bonding a cannula to a syringe barrel involves precisely positioning and then bonding the cannula to the syringe without damaging the cannula. Bends or buns in the cannula resulting from the manufacturing process can increase perceived pain of the patient. The cannula is preferably co-axial with the center or longitudinal axis of the syringe. The cannula is also preferably bonded to the syringe to withstand an approximately twenty-two Newton (22N) pull test rating in accordance with the International Standards Organization's (ISO's) standards.
The cannula of a syringe having a polymeric barrel is traditionally interference fit into a preformed barrel utilizing techniques similar to those used to manufacture syringes having glass barrels. The cannula is often affixed to the syringe by an adhesive when utilizing this method. Adhesive bonding to affix a cannula to the barrel of the syringe may be undesirable in certain situations because the adhesive may contain chemicals that could leach into the medication in the syringe. The medication may be prefilled in to the syringe, resulting in potentially prolonged exposure of the medication to the adhesive. The leaching chemicals of the adhesive may have an adverse impact on the medication/biological compound(s) maintained in the barrel of the syringe, such as altering the efficacy and/or stability of the syringe contents that eventually enter the patient.
In order to avoid the use of an adhesive, the cannula is typically crimped near its proximal end and the syringe barrel is insert molded over the proximal end of the cannula so that the syringe molds over the crimped proximal end to securely grip and retain the cannula. Though crimping the proximal end may avoid the use of an adhesive, relatively fine gauge cannulas, for example twenty-seven to thirty (27-30) gauge cannulas cannot usually be crimped without potentially damaging the cannula due to their small physical dimensions. Regardless of the attachment method, it is difficult to position, hold, and/or mount a fragile, fine gauge cannula without damaging the cannula.
It would be desirable to design, construct and employ a mechanism that holds the cannula, particularly a small diameter cannula, during the insert molding process to attach the cannula directly to a polymeric syringe barrel without the use of an adhesive or the need to crimp the cannula and without damaging the cannula. It is also desirable to construct a hub at the distal end of the barrel that effectively secures the cannula to the barrel and provides sufficient strength to withstand the operating conditions of the syringe, while utilizing a cost-effective and efficient manufacturing process.